A novel method of making PVF porous foam without using the pore forming agent

Different with the conventional method of manufacturing poly(vinyl formal) (PVF) porous foam by using the pore‐forming agents such as wheat or potato starches, a novel method without using the pore‐forming agent is introduced in this article. Through the help of images taken by a scanning electron microscope, the formation process of the present PVF foam will be discussed in terms of the spinodal decomposition (SD) phase separation principle. Additionally, the effect of poly(vinyl alcohol) concentration and reaction temperature on the pore structure of the PVF foam will be investigated. Moreover, the water adsorption capacities of the PVF foams obtained by the present method will be studied in details through the analyses of pore‐size distribution, mechanical modulus, and thermal property. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41270.     

Effects of nanosilica on retrogradation properties and structures of thermoplastic cassava starch

Composites of thermoplastic cassava starch (TPS) and nanosilica (SiO₂) were prepared by the melting method. The effect of nano‐SiO₂ on the retrogradation properties and structures of cassava starch was investigated. The retrogradation degree of TPS/nano‐SiO₂ composites increased with increasing retrogradation time. The retrogradation rate of TPS significantly increased after the addition of nano‐SiO₂, but excessive nano‐SiO₂ content leads to a decrease in the retrogradation rate of TPS. According to the Fourier transform infrared spectroscopy results, the retrogradation degree of TPS/nano‐SiO₂ composites increased with the increase of retrogradation time and addition of nano‐SiO₂. Scanning electron microscopy analysis indicated that nano‐SiO₂ particles were uniformly and finely dispersed in the starch materials, but the nano‐SiO₂ particles aggregated in the cassava starch with a further increase in nano‐SiO₂ content. X‐ray diffraction revealed that the crystalline structure of the starch was gradually altered from A‐type to V‐type with the increase of retrogradation time. TPS/SiO₂ composites indicated a mixture of A+V types, and the intensity of the V‐type strengthened with the increase of retrogradation time and SiO₂ content. Polarized light microscopy analysis revealed clear Maltese cross patterns, and the number of spherulites in TPS/nano‐SiO₂ composites increased with increasing retrogradation time and nano‐SiO₂ content, but the retrogradation of starch was inhibited with further increases of nano‐SiO₂ content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45687.     

聚乙烯醇缩甲醛吸水泡沫塑料的制备及性能研究

以淀粉为成孔剂制备了聚乙烯醇缩甲醛(PVF)泡沫塑料,研究了聚乙烯醇(PVA)种类及用量、淀粉种类及用量、甲醛与硫酸用量等因素对泡沫塑料性能的影响,并对泡沫塑料的泡孔的形态结构进行了分析。结果表明,不同成分条件下制备的泡沫塑料具有不同的密度、硬度和回弹性。该泡沫塑料是一种具有市场前景的良好的吸水材料。     

Chemical Processes During Energy‐Saving Preparation of Lightweight Ceramics

Lightweight glass‐ceramic material similar to foam glass was obtained at 700°C–800°C directly from alkali‐activated silica clay and zeolitized tuff without preliminary glass preparation. It was characterized by low bulk density of 100–250 kg/m³ and high pore size homogeneity. Chemical processes occurring in alkali‐activated silica clay and zeolitized tuff were studied using X‐ray diffraction, thermal gravimetry, IR‐spectroscopy, and scanning electron microscopy. Pore formation in both compositions is caused by dehydration of hydrated sodium polysilicates (Na₂O·mSiO₂·nH₂O), formed during alkali activation. Additional pore‐forming gas source in alkali‐activated zeolitized tuff is trona, Na₃(CO₃)(HCO₃)·2H₂O, formed during interaction between unbound NaOH and CO₂ and H₂O from air. Influence of mechanical activation of raw materials on chemical processes occurring in alkaline compositions was also studied.     

A starch‐based biodegradable film modified by nano silicon dioxide

The purpose of this work was to improve the properties of the starch/poly(vinyl alcohol) (PVA) films with nano silicon dioxide (nano SiO₂). Starch/PVA/nano‐SiO₂ biodegradable blend films were prepared by a solution casting method. The characteristics of the films were assessed by Fourier Transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). The results obtained in this study indicated that the nano‐SiO₂ particles were dispersed evenly within the starch/PVA coating and an intermolecular hydrogen bond and a strong chemical bond C? O? Si were formed in the nano‐SiO₂ and starch/PVA. That the blending of starch, PVA and nano‐SiO₂ particles led to uniform starch/PVA/nano‐SiO₂ blend films with better mechanical properties. In addition, the nano‐SiO₂ particles can improve the water resistance and light transmission of the blend films. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of a hydrophobically enhanced antifouling isotactic polypropylene/silicone dioxide flat‐sheet membrane via thermally induced phase separation for vacuum membrane distillation

Isotactic polypropylene (iPP) hydrophobic flat‐sheet membranes were fabricated for use in vacuum membrane distillation (VMD) through a thermally induced phase‐separation process with dispersing hydrophobically modified SiO₂ nanoparticles in the casting solution to achieve a higher hydrophobicity and to sustain a stable flux in VMD. The contact angle (CA) measurements indicated that the incorporation of nano‐SiO₂ into a casting solution mixture containing 20 wt % iPP had a 20.9% higher CA relative to that of SiO₂‐free membranes. The addition of nano‐SiO₂ also induced morphological changes in the membrane structure, including changes in the pore size distribution, porosity, and suppression of macrovoids. The pore size distribution of the iPP–SiO₂ membranes became narrower compared with that of the SiO₂‐free membranes, and the porosity also improved from 35.45 to 59.75% with SiO₂ addition. The average pore size and maximum pore size of the iPP–SiO₂ membranes both decreased. The ability of the membranes to concentrate an astragalus aqueous solution (a type of traditional Chinese medicine) with VMD was investigated. The surface hydrophobicity and antifouling performance of the iPP–SiO₂ membranes improved with nano‐SiO₂ addition to the membrane casting solution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42615.     

Control interfacial microstructure and improve mechanical properties of TC4-SiO2f/SiO2 joint by AgCuTi with Cu foam as interlayer

Brazing SiO_2f/SiO₂ ceramics to TC4 is often associated with the problems of excessive Ti from the dissolution of TC4 and high residual stress, which results in low-strength joints. To overcome these problems, here we put forward an effective method by introducing Cu foam as interlayer to obtain high-strength joints of SiO_2f/SiO₂-TC4. The effect of Cu foam on the microstructure and mechanical properties of brazed joints was investigated. Cu foam can consume Ti from TC4 and inhibit forming too many brittle compounds at the SiO_2f/SiO₂ side. Furthermore, Cu foam can react with Ti, forming the dispersed homogeneous distribution of fine-grained Ti-Cu compounds in the brazing seam, due to its unique 3D porous structure. The formation and distribution of fine-grained Ti-Cu compounds at the brazing seam could significantly help to reduce the residual stress and reinforce the mechanical properties of the joint. Maximum shear strength of 59.6 MPa is approached.     

Influences of molecular weight and particle morphology on film processing properties of polyvinyl fluoride

To select a suitable kind of resin for preparing films, the melting point (T_m), thermal decomposition temperature (T_d), and stretch property of polyvinyl fluoride (PVF) as a function of the viscosity–average molecular weight (M_η) were investigated. The results showed that T_d and maximal stretch ratio of extrusion‐cast PVF films gradually increase with the increase of M_η. T_m also increases when M_η is below 400,000, but keeps invariable when M_η is beyond 400,000. Six different kinds of PVF resin samples in this article were classified into three types, according to their particle morphologies: (1) loose‐structured PVF (PVF‐A and G); (2) tight‐structured PVF (PVF‐F); and (3) intermediate‐structured PVF (PVF‐B, E, and H). The effects of the morphology on the solvent absorbability of PVF were studied. The results indicated that the loose‐structured PVF has better absorption capacity to solvent than does tight‐structured PVF. The processing temperature can be considerably reduced when N,N‐dimethylformamide (DMF) as a plasticizer was mixed with PVF, and the diminished magnitude depends on the absorption capacity of PVF to DMF. The evaporation of DMF is influenced by both molecular weight and particle morphology of PVF, and the final residue of DMF in the PVF/DMF mixture is dependent on the molecular weight of PVF. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1780–1786, 2006     

Effect of the preparation conditions on the permeation of ultrahigh‐molecular‐weight polyethylene/silicon dioxide hybrid membranes

Porous ultrahigh‐molecular‐weight polyethylene/SiO₂ membranes were prepared by thermally induced phase separation (TIPS) with white mineral oil as the diluent and SiO₂ as an additive. Influential factors, including extraction method, SiO₂ content, and cooling rate, were investigated. The results suggest that the both porosity and pure water flux of the membranes by extraction of the solvent naphtha in the tension state with alcohol were the best among our research. With increasing SiO₂ content, the porosity, pure water flux, and pore diameter increased. However, with excessive SiO₂ content, defects formed easily. Moreover, SiO₂ improved the pressure resistance of the membranes. The cooling rate directly effected the crystal structure. A slow cooling rate was good for crystal growth and the integration of the diluent. Therefore, the porosity, pure water flux, and bubble‐point pore diameter increased with decreasing cooling rate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and performance of the novel PVDF ultrafiltration membranes blending with PVA modified SiO2 hydrophilic nanoparticles

In this study, PVA‐SiO₂ was synthesized by modifying silica (SiO₂) with polyvinyl alcohol (PVA), then a novel polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane was prepared by incorporating the prepared PVA‐SiO₂ into membrane matrix using the non‐solvent induced phase separation (NIPS) method. The effects of PVA‐SiO₂ particle on the properties of the PVDF membrane were systematically studied by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT‐IR), surface pore size, porosity, and water contact angle. The results indicated that with the addition of PVA‐SiO₂ particles in the PVDF UF membranes, membrane mean pore size increased from 80.06 to 126.00 nm, porosity improved from 77.4% to 89.1%, and water contact angle decreased from 75.61° to 63.10°. Furthermore, ultrafiltration experiments were conducted in terms of pure water flux, bovine serum albumin (BSA) rejection, and anti‐fouling performance. It indicated that with the addition of PVA‐SiO₂ particles, pure water flux increased from 70 to 126 L/m² h, BSA rejection increased from 67% to 86%, flux recovery ratio increased from 60% to 96%, total fouling ratio decreased from 50% to 18.7%, and irreversible fouling ratio decreased from 40% to 4%. Membrane anti‐fouling property was improved, and it can be expected that this work may provide some references to the improvement of the anti‐fouling performance of the PVDF ultrafiltration membrane. POLYM. ENG. SCI., 59:E412–E421, 2019. © 2018 Society of Plastics Engineers     

Investigation of structural order and morphology of MCM-41 mesoporous silica using an experimental design methodology

A 2⁴ factorial experiment program was carried out to study the main and interaction effects of four factors (mixture CTMABr/SiO₂, H₂O/SiO₂, and EthAc/SiO₂, and reaction time) on pore ordering, hexagonal unit cell parameter a₀, and morphology of MCM-41. The MCM-41 was synthesized from a sodium silicate solution using cetyltrimethylammonium bromide (CTMABr) surfactant and ethyl acetate (EthAc) pH modifier. None of the factors acted independently to determine pore ordering, in contrast to earlier limited literature data, which suggested a higher CTMABr/SiO₂ disturbs the assembly of the MCM-41 structure. However, there is no contradiction between these results considering that the poorly ordered product was obtained previously from a reaction mixture with the higher EthAc/SiO₂ and lower H₂O/SiO₂, which are shown to hinder pore ordering. A combination of these factors, resulting in a higher concentration of acetic acid (hydrolysis of EthAc), and thus, in a lower mixture alkalinity, implies that the pH affects pore ordering in MCM-41. This is consistent with extensive literature data on this mesoporous material. A small (up to ∼5%) variation of a₀ due to the reaction composition and time variation was insignificant compared to the reported doubling of a₀ caused by the effects of varying the surfactant alkyl chain length, addition of swelling organic compounds, or hydrothermal restructuring. Particle morphology (hexagonal platelets, gyroids, and crescent-like or worm-shaped particles) depended on the combination of mixture CTMABr/SiO₂, H₂O/SiO₂, and EthAc/SiO₂. This is consistent with the literature evidence that morphogenesis of hexagonally ordered silica is a complex phenomenon involving a variety of reaction variables.     

Effect of SiO2 on rheology,morphology, thermal,and mechanical properties of high thermal stable epoxy foam

A series of highly thermostable epoxy foams with diglycidyl ether of bisphenol‐A and bisphenol‐S epoxy resin (DGEBA/DGEBS), 4,4′‐diaminodiphenyl sulfone (DDS) as curing agent have been successfully prepared through a two‐step process. Dynamic and steady shear rheological measurements of the DGEBA/DGEBS/DDS reacting mixture are performed. The results indicate all samples present an extremely rapid increase in viscosities after a critical time. The gel time measured by the crossover of tan δ is independent of frequency. The influence of SiO₂ content on morphology, thermal, and mechanical properties of epoxy foams has also been investigated. Due to the heterogeneous nucleation of SiO₂, the pore morphology with a bimodal size distribution is observed when the content of SiO₂ is above 5 wt %. Dynamic mechanical analysis (DMA) reveals that pure epoxy foam possesses a high glass transition temperature (206°C). The maximum of specific compressive strength can be up to 0.0253 MPa m³ kg^?1 at around 1.0 wt % SiO₂. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40068.     

Highly porous Y2SiO5 ceramic with extremely low thermal conductivity prepared by foam‐gelcasting‐freeze drying method

Foam‐gelcasting‐freeze drying method is developed to fabricate porous Y₂SiO₅ ceramic with ultrahigh porosity of 92.2%‐95.8% and isotropous multiple pore structures. As prepared porous samples have quite low shrinkages of 0.8%‐1.9% during demolding and drying processes, lightweights of 0.19‐0.35 g/cm³, and extremely low thermal conductivities of 0.054‐0.089 W·(m·K)^?1. Our approach combines the merits of foam‐gelcasting method and freeze drying method. It is a simple and effective method to fabricate porous ceramics with very high porosity and extremely low thermal conductivity through low shrinkage of green body and near net complex shape forming.     

Microencapsulated melamine phosphate via the sol–gel method and its application in halogen‐free and intumescent flame‐retarding acrylonitrile‐butadiene‐styrene copolymer

In this paper, a facile method is introduced to modify melamine phosphate (MP) via the sol–gel process. The aim was simultaneously to increase the water resistance of MP and improve the dispersion and compatibility of MP in acrylonitrile‐butadiene‐styrene copolymer (ABS). In addition, the incorporation of SiO₂ particles into the MP/dipentaerythritol (DPER) system can further ameliorate the char‐forming ability and enhance the flame retardant properties of polymer composites. The chemical structure and surface morphology of SiO₂@MP were confirmed and observed by Fourier transform infrared (FTIR) spectroscopy, SEM and TEM, respectively. The results demonstrate that ABS/SiO₂@MP/DPER (3/1) at a loading of 30 phr reaches 31.2% limiting oxygen index and achieves a UL‐94 V‐0 rating. Moreover, FTIR spectra indicate that the main char‐forming process of the SiO₂@MP/DPER system occurs at 365–420 °C. A potential condensed flame retardant mechanism of SiO₂@MP and DPER in ABS composites is proposed via the systematic analysis of char residue after combustion by FTIR spectroscopy, SEM and X‐ray photoelectron spectroscopy. © 2015 Society of Chemical Industry     

A novel natural rubber‐graft‐cassava starch foam for oil/gasohol absorption

The objective of this work was to study a novel foam prepared from natural rubber grafted with cassava starch (NR‐graft‐CSt) with the addition of super cell (SC) as a blowing agent. The effects of the blowing agent and grafting versus non‐grafting of the starch and the natural rubber on the properties of the foam were investigated. The results show that the optimum curing time decreases with increasing SC loading as observed using a moving die rheometer. The porosity, the number of cells per unit volume and the cell size of the NR/CSt blend increase as a function of the SC loading in the foam. A more open cell structure is produced by higher loadings of SC. The greatest number of cells per unit volume is found at 2 and 6 phr SC for NR‐graft‐CSt and NR/CSt blend, respectively. The foam produced was used as an absorbent for oil. The NR‐graft‐CSt foam shows a maximum percentage oil absorption of around 7 g g^?1. The NR‐graft‐CSt foam is able to be reused as an oil absorbent for a maximum number of over 30 times. The NR‐graft‐CSt foam shows better toluene resistance than the NR/CSt blend. © 2016 Society of Chemical Industry     

Preparation and properties of nylon 6/carboxylic silica nanocomposites via in situ polymerization

Nylon 6/carboxylic acid‐functionalized silica nanoparticles (SiO₂‐COOH) nanocomposites were prepared by in situ polymerization of caprolactam in the presence of SiO₂‐COOH. The aim of this work was to study the effect of carboxylic silica on the properties of the nylon 6 through the interfacial interactions between the SiO₂‐COOH nanoparticles and the nylon 6 matrix. For comparison, pure nylon 6, nylon 6/SiO₂ (unmodified) and nylon 6/amino‐functionalized SiO₂ (SiO₂‐NH₂) were also prepared via the same method. Fourier transform infrared spectrometer (FTIR) spectroscopy was used to evaluate the structure of SiO₂‐COOH and nylon 6/SiO₂‐COOH. The results from thermal gravimetric analysis (TGA) indicated that decomposition temperatures of nylon 6/SiO₂‐COOH nanocomposites at the 5 wt % of the total weight loss were higher than the pure nylon 6. Differential scanning calorimeter (DSC) studies showed that the melting point (T_m) and degree of crystallinity (X_c) of nylon 6/SiO₂‐COOH were lower than the pure nylon 6. Mechanical properties results of the nanocomposites showed that nylon 6 with incorporation of SiO₂‐COOH had better mechanical properties than that of pure nylon 6, nylon 6/SiO₂, and nylon 6/SiO₂‐NH₂. The morphology of SiO₂, SiO₂‐NH₂, and SiO₂‐COOH nanoparticles in nylon 6 matrix was observed using SEM measurements. The results revealed that the dispersion of SiO₂‐COOH nanoparticles in nylon 6 matrix was better than SiO₂ and SiO₂‐NH₂ nanoparticles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Silica/polystyrene and silica/polystyrene‐b‐polymethacryloxypropyltrimethoxysilane hybrid nanoparticles via surface‐initiated ATRP and comparison of their wettabilities

Both silica/polystyrene (SiO₂/PS) and silica/polystyrene‐b‐polymethacryloxypropyltrimethoxysilane (SiO₂/PS‐b‐PMPTS) hybrid nanoparticles were synthesized via surface‐initiated atom transfer radical polymerization (SI‐ATRP) from SiO₂ nanoparticles. The growths of all polymers via ATRP from the SiO₂ surfaces were well controlled as demonstrated by the macromolecular characteristics of the grafted chains. Their wettabilities were measured and compared by water contact angle (WCA) and surface roughness. The results show that the nanoparticles possess hydrophobic surface properties. The static WCA of SiO₂/PS‐b‐PMPTS hybrid nanoparticles is smaller than that of SiO₂/PS hybrid nanoparticles, meanwhile, the surface roughness of SiO₂/PS‐b‐PMPTS hybrid nanoparticles is yet slightly rougher than that of SiO₂/PS hybrid nanoparticles, which shows that the combination and competition of surface chemistry and roughness of a solid material can finally determine its wettability. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Preparation and properties of hydrophobic poly(vinylidene fluoride)–SiO2 mixed matrix membranes for dissolved oxygen removal from water

The application of the membrane method for removing dissolved oxygen (DO) from water on the laboratory scale was studied. Flat mixed matrix membranes were composed of poly(vinylidene fluoride) (PVDF) and hydrophobic nanosilica particles, which were used to improve the DO removal process. The SiO₂ particles were modified by a silane coupling agent and examined by Fourier transform infrared spectroscopy. It was shown that the surface of the SiO₂ particles was bonded to hydrophobic long‐chain alkane groups through chemical bonding. The effects of adding SiO₂ particles on the membrane properties and morphology were examined. The results show that the porosity and pore size of the membrane were affected by the introduction of SiO₂ particles, and the cross‐sectional morphology of the PVDF composite membranes changed from fingerlike macrovoids to a spongelike structure. The membrane performance of DO removal was evaluated through the membrane unit by a vacuum degassing process. It was found that the SiO₂/PVDF hybrid membranes effectively improved the oxygen removal efficiency compared with the original PVDF membranes. The maximum permeation flux was obtained when the loading amount was 2.5 wt %. The effect of the downstream vacuum level was also investigated. The experimental results show that the SiO₂/PVDF hybrid membranes had superior performances and could be an alternative membrane for removing DO from water. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40430.     

Investigation on polyimide/silica hybrid foams and their erosion resistance to atomic oxygen

A series of polyimide/silica (PI/SiO₂) hybrid foams were prepared by the sol–gel process. Aminopropyltriethoxysilane was used as the coupling agent to enhance the compatibility between PI matrix and SiO₂. Fourier transform infrared spectroscopy and scanning electron microscopy were used to analyze the chemical structure and cellular structure of PI/SiO₂ hybrid foams. The results indicated that the three‐dimensional network of Si O Si was formed in the hybrid foams, and the hybrid foam presented the uniform cellular structure when the SiO₂ content was less than 6 wt%. The thermal stability, dynamic mechanical property, and dielectric property of PI/SiO₂ hybrid foams were investigated by dynamic mechanical analysis, thermogravimetric analysis, and vector network analyzer, respectively. The introduction of SiO₂ improved the thermal stability and increased the storage modulus and glass‐transition temperature. The hybrid foams showed higher dielectric constants compared with the neat PI foam. The erosion resistance to atomic oxygen (AO) of PI/SiO₂ hybrid foams was also evaluated in a ground‐based AO simulator. The surface morphology and chemical structure of PI/SiO₂ hybrid foams before and after AO exposure were investigated by scanning electron microscopy, atomic force microscopy, and X‐ray photoelectron spectroscopy. The results revealed that the inorganic SiO₂ protective layers were formed on the surface of PI/SiO₂ hybrid foams after AO exposure, which could effectively improve the AO erosion resistance of PI/SiO₂ hybrid foams. POLYM. COMPOS., 36:713–721, 2015. © 2014 Society of Plastics Engineers     

Preparation of Micro‐/Mesoporous SiOC Bulk Ceramics

Micro‐/mesoporous SiOC bulk ceramics with high surface area and bimodal pore size distribution were prepared by pyrolysis of polysiloxane in argon atmosphere at 1100°C–1400°C followed by etching in hydrofluoric acid solution. Their thermal behaviors, phase compositions, and microstructures at different nano‐SiO₂ filler contents and pyrolysis temperatures were investigated by XRD, SEM, DSC, and BET. The SiO₂ fillers and SiO₂‐rich clusters in the SiOC matrix act as pore‐forming sites and can be etched away by HF. At the same time, the SiO₂ filler promotes SiOC phase separation during the pyrolysis. The filler content and pyrolysis temperature have important effects on phase compositions and microstructures of porous SiOC ceramics. The resulting porous SiOC bulk ceramic has a maximum specific surface area of 822.7 m²/g and an average pore size of 2.61 nm, and consists of free carbon, silicon carbide, and silicon oxycarbide phases.